Introduction

Soft drinks are the beverage of choice for millions of Americans. Some drink them morning, noon, night, and in between. They’re tasty, available everywhere, and inexpensive. They’re also a prime source of extra calories that can contribute to weight gain. Once thought of as innocent refreshment, soft drinks are also coming under scrutiny for their contributions to the development of type 2 diabetes, heart disease, and other chronic conditions. Diet soft drinks, made with artificial sweeteners, may not be the best alternatives to regular soft drinks.

The term “soft drink” covers a lot of ground. It refers to any beverage with added sugar or other sweetener, and includes soda, fruit punch, lemonade and other “ades,” sweetened powdered drinks, and sports and energy drinks. In this section of The Nutrition Source, we focus on non-alcoholic sweetened drinks.

Drunk every now and then, these beverages wouldn’t raise an eyebrow among most nutrition experts, any more than does the occasional candy bar or bowl of ice cream. But few people see them as treats. Instead, we drink rivers of the stuff.

According to figures from the beverage industry, soft drink makers produce a staggering 10.4 billion gallons of sugary soda pop each year. (1) That’s enough to serve every American a 12-ounce can every day, 365 days a year.

The average can of sugar-sweetened soda or fruit punch provides about 150 calories, almost all of them from sugar, usually high-fructose corn syrup. That’s the equivalent of 10 teaspoons of table sugar (sucrose). If you were to drink just one can of a sugar-sweetened soft drink every day, and not cut back on calories elsewhere, you could gain up to 15 pounds in a year.

Soft Drinks and Weight

Historians may someday call the period between the early 1980s and 2009 the fattening of America. Between 1985 and now, the proportion of Americans who are overweight or obese has ballooned from 45 percent in the mid-1960s to 66 percent today. (The Centers for Disease Control and Prevention has an online slide show that shows the spread of obesity in the U.S.) There’s no single cause for this increase; instead, there are many contributors. One of them is almost certainly our penchant for quenching our thirst with beverages other than water.

Once upon a time, humans got almost all of their calories from what nature put into food. That changed with the advent of cheap sugar, and then cheaper high-fructose corn syrup. High-fructose corn syrup has been fingered as one of the villains in the obesity epidemic, (2) but in fact, table sugar and corn sweeteners likely have the same physiological impact on blood sugar, insulin, and metabolism. Sugar added to food now accounts for nearly 16 percent of the average American’s daily intake. Sweetened soft drinks make up nearly half of that. (3)

Dozens of studies have explored possible links between soft drinks and weight. It isn’t an easy task, for several reasons (read Sorting Out Studies on Soft Drinks and Weight to learn why). Despite these research challenges, studies consistently show that increased consumption of soft drinks is associated with increased energy intake. In a meta-analysis of 30 studies in this area, 10 of 12 cross-sectional studies, five of five longitudinal studies, and four of four long-term experimental studies showed this positive association. (3) A different meta-analysis of 88 studies showed that the effect appeared to be stronger in women, studies focusing on sugar-sweetened soft drinks, and studies not funded by the food industry. (4) Studies in children and adults have also shown that cutting back on sugary drinks can lead to weight loss. (5, 6)

On the surface, it makes sense that the more ounces of sugar-rich soft drink a person has each day, the more calories he or she takes in. Yet that runs counter to what happens with solid foods. People tend to compensate for a bigger than usual meal or for a snack by taking in fewer calories later. That’s how weight stays stable. This compensation doesn’t seem to happen with soft drinks. No one knows for sure why this happens, but there are several possibilities:

Fluids may not be as satiating as solid foods. That means they don’t provide the same feeling of fullness or satisfaction that solid foods do, which might prompt you to keep eating.

The body doesn’t seem to “register” fluid calories as carefully as it does those from solid food. This would mean they are added on top of calories from the rest of the diet. (7)

It is possible that sweet-tasting soft drinks—regardless of whether they are sweetened with sugar or a calorie-free sugar substitute—might stimulate the appetite for other sweet, high-carbohydrate foods.

How Much is too much added sugar?

Some sources of carbohydrate are healthier than others, and sugar added to foods and drinks falls into the less-healthy group—no matter whether it’s table sugar or brown sugar, honey or high-fructose corn syrup, or any other type of added sugar. A good goal is keeping added sugars from all sources to under 10 percent of your daily calories. But remember—your body doesn’t need to get any carbohydrate from added sugar. That’s why the Healthy Eating Pyramid says sugary drinks and sweets should be used sparingly, if at all.Learn how to find added sugar on a food label.

Soft Drinks and Diabetes

Gulping the equivalent of 10 teaspoons of sugar over the course of a few minutes gives the body’s blood sugar controls a run for their money. Most people handle a blast of blood sugar just fine. Over time, though, a diet rich in easily digested carbohydrates may lead to type 2 diabetes (once called non-insulin-dependent diabetes and adult-onset diabetes).

Strong evidence indicates that sugar-sweetened soft drinks contribute to the development of this potentially disabling disease. The Nurses’ Health Study explored this connection by following the health of more than 90,000 women for eight years. The nurses who said they had one or more servings a day of a sugar-sweetened soft drink or fruit punch were twice as likely to have developed type 2 diabetes during the study than those who rarely had these beverages. (8)

A similar increase in risk of diabetes with increasing soft drink and fruit drink consumption was seen recently in the Black Women’s Health Study, an ongoing long-term study of nearly 60,000 African-American women from all parts of the United States. (9) Interestingly, the increased risk with soft drinks was tightly linked to increased weight.

In the Framingham Heart Study, men and women who had one or more soft drinks a day were 25 percent more likely to have developed trouble managing blood sugar and nearly 50 percent more likely to have developed metabolic syndrome. This is a constellation of factors—high blood pressure; high insulin levels; excess weight, especially around the abdomen; high levels of triglycerides; and low levels of HDL (good) cholesterol—that is one step short of full blown diabetes and boosts the odds of developing heart disease. (10)

Soft Drinks and Heart Disease

Obesity and diabetes are both strong risk factors for heart disease, the number one killer of men and women in the U.S. Given that drinking sugary beverages increases the risk of both obesity and diabetes, it is a natural question to ask whether drinking sugary beverages increases the risk of heart disease, too.

The answer from the first long-term study to ask that question is a resounding yes: The Nurses’ Health Study, which tracked the health of nearly 90,000 women over two decades, found that women who drank more than two servings of sugary beverage each day had a 40 percent higher risk of heart attacks or death from heart disease than women who rarely drank sugary beverages. (11)

Of course, people who drink a lot of sugary drinks often tend to weigh more—and eat less healthfully—than people who don’t drink sugary drinks, and the volunteers in the Nurses’ Health Study were no exception. But researchers accounted for differences in diet quality, energy intake, and weight among the study volunteers. They found that having an otherwise healthy diet, or being at a healthy weight, only slightly diminished the risk associated with drinking sugary beverages.

This suggests that weighing too much, or simply eating too many calories, may only partly explain the relationship between sugary drinks and heart disease. The adverse effects of the high glycemic load from these beverages on blood glucose, cholesterol fractions, and inflammatory factors probably also contribute to the higher risk of heart disease. The glycemic load is a way to classify foods that takes into account both the amount and the quality of the carbohydrates that they contain. Foods that are high in rapidly digested carbohydrate—a can of sugary soda pop, a handful of jelly beans, a plateful of pasta—have a high glycemic load. Eating a diet rich in high-glycemic-load foods may, over time, lead to type 2 diabetes, heart disease, and other conditions. Learn more about the glycemic load and health.

Soft Drinks and Bones

There’s also some concern about the impact of soft drinks on building bone and keeping it strong and healthy. There is an inverse pattern between soft drinks and milk—when one goes up, the other goes down. (4) Trading milk for soft drinks isn’t a good swap. Milk is a good source of calcium and protein, and also provides vitamin D, vitamin B6, vitamin B12, and other micronutrients (of course you can drink too much milk, too; see Calcium and Milk: What’s Best for Your Bones and Health, for more information). Soft drinks are generally devoid of calcium and other healthful nutrients. And just adding vitamins and minerals to sugar water does not make a healthy drink. Getting enough calcium is extremely important during childhood and adolescence, when bones are being built. Yet soft drinks are actively marketed to these age groups, and they are key consumers of sugar-sweetened beverages.

Cola-type beverages may pose a special challenge to healthy bones. Colas contain high levels of phosphate. On the surface, this sounds like a good thing, because bone needs both calcium and phosphate. But getting much more phosphate than calcium can have a deleterious effect on bone. (3)

What About Diet Soft Drinks? Artificial Sweeteners and Weight Control

Using artificial sweeteners in soft drinks instead of sugar or high-fructose corn syrup seems like it would sidestep any problems with weight or diabetes. Artificial sweeteners deliver zero carbohydrates, fat, and protein, so they can’t directly influence calorie intake or blood sugar. Over the short term, switching from sugar-sweetened soft drinks to diet drinks cuts calories and leads to weight loss. Long-term use, though, may be a different story.

To date, the FDA has approved the use of five artificial sweeteners. Gram for gram, each one is far sweeter than sugar. (12) They include:

One natural low-cal sweetener, stevia, has not yet been evaluated by the FDA. Stevia is a non-caloric sweetener made from the leaves of a shrub that grows in South and Central America. Its manufacturers say that it is safe; while the FDA has not done its own safety evaluation, it has not objected to these safety findings, (13) paving the way for stevia’s incorporation into foods and drinks. Stevia is about 300 times sweeter than sugar. Early reports that stevia might cause cancer had made the FDA demand more information from manufacturers about its safety. A number of major soft drink companies have begun launching stevia-sweetened beverages, sometimes combining stevia with erythritol, a sugar alcohol. There are no long-term studies of the health effects of stevia, however, so drinkers beware.

Erythritol and xylitol are sugar alcohols, a class of compounds that have been used for decades to sweeten chewing gum, candy, fruit spreads, toothpaste, cough syrup, and other products. Newer, cheaper ways to make sugar alcohols from corn, wood, and other plant materials, along with their sugar-like taste, are fueling their use in a growing array of foods.

Some long-term studies show that regular consumption of artificially sweetened beverages reduces the intake of calories and promotes weight loss or maintenance. Others show no effect, while some show weight gain. (12)

One worry about artificial sweeteners is that they uncouple sweetness and energy. Until recently, sweet taste meant sugar, and thus energy. The human brain responds to sweetness with signals to, at first, eat more and then with signals to slow down and stop eating. By providing a sweet taste without any calories, artificial sweeteners could confuse these intricate feedback loops that involve the brain, stomach, nerves, and hormones. If this happens, it could throw off the body’s ability to accurately gauge how many calories are being taken in.

Studies in rats support this idea. Purdue University researchers have shown that rats eating food sweetened with saccharin took in more calories and gained more weight than rats fed sugar-sweetened food. (14) A long-term study of nearly 3,700 residents of San Antonio, Texas, showed that those who averaged three or more artificially sweetened beverages a day were more likely to have gained weight over an eight-year period than those who didn’t drink artificially sweetened beverages. (15) Although this finding is suggestive, keep in mind that it doesn’t prove that artificially sweetened soft drinks caused the weight gain.

Imaging studies support the idea that sugar and artificial sweeteners affect the brain in different ways. Some parts of the brain become activated when we experience a “food reward.” At the University of California-San Diego, researchers performed functional MRI scans as volunteers took small sips of water sweetened with sugar or sucralose. Sugar activated regions of the brain involved in food rewards, while sucralose didn’t. (16) So it is possible, the authors say, that sucralose “may not fully satisfy a desire for natural caloric sweet ingestion.” More research is needed to tease out the implications of these findings for weight control.

Although the scientific findings are mixed and not conclusive, there is worrisome evidence that regular use of artificial sweeteners may promote weight gain. Because of these mixed findings about artificial sweeteners, drinking diet soda may not be the best replacement for drinking sugary soda.

The Bottom Line: Skip Sugary Drinks and Go Easy on Diet Drinks

So what’s the best choice for your health? For adults and children, the evidence is strong that cutting back on sugary drinks—or eliminating them altogether—may help with weight control and will almost surely lower the risk of diabetes. There’s emerging evidence that sugary drinks increase the risk of heart disease. The evidence is less clear-cut for artificially sweetened drinks. For adults trying to wean themselves from sugary soda, diet soda may be the beverage equivalent of a nicotine patch: something to be used in small amounts, for a short time, just until you kick the habit. For children, the long-term effects of consuming artificially-sweetened beverages are unknown, so it’s best for kids to avoid them.

Healthier drinking is not just an individual problem. Beverage makers have flooded the market with drinks that offer gobs of sugar, or an unpronounceable list of artificial sweeteners. What’s sorely lacking in the beverage marketplace is a middle ground—a drink for people who want just a little bit of sweetness, but don’t want too much sugar, and want to shy away from artificial sweeteners or stevia because of health concerns.

There are very few beverages on the market that have no more than 1 gram of sugar per ounce, without any other type of sweetener—sweet enough to please the palate but, at 50 calories per 12-ounce can, not so hard on the waistline, as long as they are drunk in moderation. That’s why researchers at Harvard School of Public Health have suggested that beverage manufacturers introduce more of these lightly sweetened drinks to the market, to help Americans retrain their palates away from sweet drinks.

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